1. Field of the Invention
This invention relates to apparatus for continuously treating a cord that can be incorporated into a power transmission belt and, more particularly, to a processing liquid application system through which processing liquid is continuously applied to the cord.
2. Background Art
It is known to use load carrying cords in all types of power transmission belts, i.e. V-belts, V-ribbed belts, toothed belts, etc., and particularly those used in industrial applications. Typically, the cords are made from fiber material, such as polyester fiber, aramid fiber, glass fiber, and the like. To improve adhesion with the belt rubber, it is known to pretreat the fiber cords. For example, it is known to treat the cords with a resorcinol formalin latex (RFL) alone or to use the RFL treatment after pretreating the cords with an epoxy or isocyanate compound. It is also known to adhere rubber gum after the RFL treatment.
There are currently in use apparatus through which a cord is continuously drawn off of a supply at a fixed tension and through a supply of adhesive liquid in a dip tank reservoir and moved into an oven in which the adhesive liquid is dried. It is also known to move the treated cord outside of the oven, where it is cooled and subsequently caused to undergo repeated similar processing steps. The subsequent processing steps may be carried out using different processing liquids, different heating temperatures in drying ovens, and different cord tension during processing so as to give the belt the desired optimal properties for incorporation into a power transmission belt. Once the processing is completed, the cord can be continuously accumulated on a take-up unit.
It is known to splice multiple supplies of the cord together so that the overall apparatus can continuously treat the cord without interruption. This can be accommodated at the collection end of the apparatus by incorporating multiple take-up units.
To accommodate this type of continuous operation, it is necessary to keep a sufficient supply of processing liquid in dip tank reservoirs. It is known to provide a bulk supply container in association with each dip tank. High and low level detection switches are provided to automatically control the discharge of the processing liquid from the supply container to the dip tank. An automatic switching valve is closed by one switch when the level reaches a "full" height, with a separate switch being operated to open the switching valve when the liquid reaches a "low level" height.
With this type of system, there may be a significant difference between the "full" and "low" level heights of processing liquid in the dip tanks. As a result, there is a significant difference in immersion time for a continuously advancing cord as it moves through the liquid at the two different heights. The amount of processing liquid adhered to the cord may thus vary from one length to the next. As a result, the cord properties may significantly change from one length to the next.
To avoid a situation where less than the desired amount of processing liquid is adhered to the cord, it is known to keep a surplus amount of processing liquid in the dip tanks. This may result in an increase in the cost of operating the system.
Since the processing liquid solvents may have rubber or resin as a base material, after long periods of operation, these materials solidify. This is particularly a problem around the closing valve, which may become clogged and inoperable or ineffectively operable.
Further, because the processing liquids often contain organic solvents such as toluene, to avoid fire and undesired contact with system operators, it is known to use explosion-proof components on the level switches and closing valves that come in contact with the processing liquid. These modifications often result in increased system size and weight. Further, equipment costs may rise due to all the modifications necessary to make the system operate safely and efficiently. These modifications may make setup, repair, and maintenance, more difficult and costly to perform. Safety compromises may also result in operation and maintenance of these systems.
In recent years, there has been a trend towards having more system flexibility in terms of the processing liquid used and the variation in processing steps. At the same time, there has been a demand for small volume production with this flexibility. Accordingly, the need for a solution to the above-mentioned problems exists.